"We have inherited a somewhat dissatisfied group of partners who are dissatisfied with us, who have slowed deployments," Mr Switkowski said later.

"There's no change in the current strategy. We are rolling out fibre to the premises where we can.

"We have a machine ... that is running at four or five thousand (homes) a week, which it was during Senator Conroy's time."

The coalition on Thursday released a strategic review of the NBN, which found that under Labor's plans, the rollout would miss its 2021 target by three years and cost $73 billion - up from $43 billion - to complete.

Mr Switkowski said the rollout had been largely scattered, and involved many contractors doing subcritical work.

The committee heard that divisions within NBN Co were providing different sets of figures on the same subject.

The review also found the government would not be able to meet its pledge of delivering 25 Mbps to all Australians by 2016, and its NBN plans would cost 40 per cent more than the $29.5 billion estimated in April.

Mr Turnbull said the coalition remained committed to limiting its equity investment in NBN Co to $29.5 billion, with the excess cost to be made up through debt.

Positive cashflow from NBN Co to pay off that debt is estimated to emerge in 2022.